Delta-sigma modulators are used in circuits, such as phase-locked loops, over a wide range of frequencies for functions like analog-to-digital conversion. Delta-sigma analog-to-digital converters (ΔΣ ADCs) are used in applications like voiceband, audio, and other high-resolution precision applications. A ΔΣ ADC can be used over a wide range of frequencies by using an oversampling modulator followed by a filter to produce a high-resolution data-stream output. Some advantages associated with ΔΣ modulators include high dynamic range and the ability to shape quantization noise out-of-band. A ΔΣ ADC operates by receiving an input analog signal, oversamples the signal, and accumulates the same portion over time to produce an output digital signal. A digital filter can sample the output signal of the ΔΣ ADC to produce a desired digital signal. Delta-sigma modulators can use switched-capacitor functional blocks, such as one or more switched-capacitor integrators and/or switched-capacitor summers.
Delta-sigma modulators can be configured to possess more advanced characteristics, such as noise shaping to reduce noise at lower frequencies. For conventional feed-forward ΔΣ modulators, a design that achieves Nth-order noise shaping at its output requires its circuit configuration to include N+1 operational amplifiers (op-amps). Thus, for a ΔΣ modulator to achieve third-order noise shaping, the circuit architecture would require use of four op-amps.
When designing power-efficient ΔΣ modulators, factors like size, power consumption, speed, and production costs are part of the design considerations. Depending on the desired characteristics, operational amplifiers can be major, complex components that can largely direct the cost and size of ΔΣ modulators used in electronic circuits.
In view of the foregoing, it would be desirable to improve design of delta-sigma modulators. In particular, it would be desirable to modify the architecture of noise-shaping ΔΣ modulators to more efficiently use power.